Since 1985, scientists have been monitoring a hole in the ozone layer, high above Antarctica. It had been hoped that the ozone hole will gradually shrink, but new results from ESA’s Envisat spacecraft have revealed the highest ozone loss on record.

Measurements made on 2 October showed a loss of 40 million tonnes, beating the previous record in the year 2000. In addition, this year’s ozone hole covers an area of 28 million square km, nearly as large as the hole of 2000. The depth of the ozone hole also rivals previous record values.

“Such significant ozone loss requires very low temperatures in the stratosphere, combined with sunlight,” said ESA scientist Claus Zehner. “This year’s extreme loss of ozone can be explained by the temperatures above Antarctica reaching about minus 92 Celsius - the lowest recorded in the area since 1979.”

Ozone loss over the South Pole

Ozone is a type of oxygen gas. It forms a layer 25 – 40 km above the Earth in a region known as the stratosphere. The ozone layer is important because it blocks harmful ultraviolet rays from the Sun. These rays increase the risk of skin cancer and eye cataracts, and affect marine life.

The thinning of the ozone is caused by human-made pollutants, such as chlorine, which stay in the atmosphere for many years. When the polar spring arrives, sunlight releases chlorine trapped in high-level clouds. Chlorine then rapidly destroys the ozone.

The hole usually lasts until November or December, when ozone-poor air above Antarctica begins to mix with ozone-rich air from outside.